Miriam L. Schmitt U.S. Pat. No. 5,099,858 (which is incorporated herein by reference), I described and claimed a device useful for measuring the Pulfrich stereo-illusion phenomenon in people with normal vision and without ocular and optic nerve disease and for diagnosing ocular and optic nerve disease in people who are capable of experiencing that phenomenon. I also described and claimed a method of measurement utilizing my novel device.
My present invention is a further advance in technology and resides in making a video recording comprising a series of repeating segments, each segment showing the ballerina and cone as described in my issued patent. The person to be tested views the video and follows the audio instructions. Data is recorded and the measurements are assessed by an ophthalmologist to determine the condition of the eyes of the person being tested. When the video is shown on a television receiver or monitor, the accuracy of the measurements are greatly enhanced by superimposing a cone on the exterior viewing surface over the cone as it is shown in the recorded segments.
The Pulfrich stereo-illusion is a psychophysical response dependent on stereoscopic binocular central vision. The Pulfrich stereo-illusion phenomenon of a frontal plane oscillating object appearing to travel in an elliptical orbit when viewed with unequal binocular illumination was described in 1922 by Carl Von Pulfrich, a German scientist. Viewed from above, the direction of the orbit is clockwise when the image perceived by the left eye is dimmer and counter-clockwise when the image perceived by the right eye is dimmer. The apparent depth of the orbit has been found to vary the difference in the binocular retinal illumination, and the distance from the observer to the pendulum bob, and inversely with the background illumination level.
Pulfrich postulated that the stereo effect resulted from a prolonged latent period of vision along the afferent pathway of the eye perceiving the dimmer image. Subsequent investigators using the episcotistor, random dot stereo-movies, and visual-evoked responses, have confirmed that the latent period of vision increases as the retinal illumination decreases. The synchronous conduction of impulses originating from corresponding retinal points produces disparity in the simultaneous perception of these stereo-pairs and hence the false sensation of depth to the viewer.
The minimum visual and stereoscopic acuities required to appreciate the normal stereo-illusion were first described by me in "Clinical Applications of the Pulfrich Phenomenon" in Ocular Inflammation Ther. 1:117-123 (1983) and in my EPA 87402784.0 published Jun. 15, 1988.
It has been suggested in the literature that the appreciation of the Pulfrich stereo-illusion depends not only on normal vision, but also upon the skill of the individual as an observer. Consequently, the inability to induce the normal stereo-illusion by placing a filter before one eye has not been considered a sign of disease since factors other than visual acuity and stereopsis have been thought to influence the appreciation of the stereo-illusion. However, using my device, I have shown that all normal sighted persons are able to see the stereo-illusion under the testing conditions described in my U.S. Pat. No. 5,099,858.
Utilizing the Pulfrich stereo-illusion, I developed a device I call the stereo-photometer for determining the presence of diseases affecting the visual system which interferes with central acuity, stereopsis, or the brightness equality of the images perceived by the right and left visual pathways. This has been described and claimed in my U.S. Pat. No. 5,099,858. Reduced perceived brightness can be the result of pre-retinal, retinal, or optic nerve disease. Regardless of the anatomical site responsible for the brightness imbalance of the right and left visual pathways, the correct neutral density filter positioned before the eye perceiving the brighter image will bring the right and left visual pathways into balance. In the development of the stereo-photometer, I have applied the Pulfrich stereo-illusion principle as a sensitive brightness balance to compare and measure the visual input to the right and left visual pathways. The stereo-photometer is designed to precisely control and measure the luminance to each eye with variable neutral density filters while maintaining constant all other variables known to affect the stereo-illusion. The luminance difference between the two eyes (interocular) can be calculated from the measured luminance to each eye.
The stereo-illusion is a normal phenomenon only when occurring within a certain range of interocular luminance differences. A disease of the visual system is present when: (1) the stereo-illusion is seen by the subject without attenuating the luminance to either eye (spontaneous response), (2) the luminance attenuation to induce the stereo-illusion is different for each eye and outside the normal range (asymmetric induced response), (3) the luminance attenuation to neutralize an induced stereo-illusion created with a standard value neutral density filter is different for each eye and outside the normal range (asymmetric neutralization response), (4) a subthreshold neutral density filter placed before one but not the other eye induces the stereo-illusion, or (5) the stereo-illusion cannot be induced at any interocular luminance difference (non-inducible response).
The spontaneous response has a specific orientation which dictates the pathway perceiving the dimmer image, i.e., clockwise for the left pathway and counter-clockwise for the right pathway. Testing with the stereo-photometer, the spontaneous response can be precisely quantitated by balancing the brightness disparity between the right and left visual pathways with the progressive neutral density filter before the eye perceiving the brighter image until the endpoint is reached. The endpoint is the moment the pendulum bob motion changes from rotational about a reference point to planar.
The spontaneous response is seen by the person without altering the ambient viewing conditions and occurs when the brightness disparity between the right and left visual pathways exceed a threshold difference. This happens in pre-retinal diseases causing unequal pupils of media opacities, retinal diseases causing neuronal dysfunction within the retina, or optic nerve disease causing delay nerve conduction velocity as I reported in "Clinical Application of the Pulfrich Phenomenon," Ocular Inflammation Ther. 1:117-123 (1983) and "Pulfrich Stereo-Illusion Phenomenon in Serous Sensory Retinal Detachment of the Macula," Amer. J. Ophthalmol. 100:576-580 (1985) and in my EPA 87402784.0, published Jun. 15, 1988.
Disease conditions exist in which the brightness appreciation is less in one visual pathway than the other but not to the degree that produces the spontaneous response. This subthreshold brightness disparity can be detected by the induction or neutralization technique. If the brightness appreciation is unequal for the two sides, the induction or neutralization endpoints will be different for each side and the larger the interocular difference the more the brightness disparity. An alternative induction technique to detect a subthreshold brightness defect is to use a neutral density filter of less density than required to induce the stereo-illusion in normal sighted people. Placing this sub-threshold filter before the eye with the subthreshold defect the combination will result in an interocular difference of the threshold level for the stereo-illusion. When this same subthreshold filter is placed before the opposite eye, threshold level cannot be reached since that eye must be functioning at a high relative brightness level and would require a filter of higher density than required to induce the stereo-illusion in a normal sighted person.
The use of a cone as the reference point and a ballerina is important in maximizing the stereo-illusion effect for the observer.
I discovered that a cone is a particularly useful fixation target and that a ballerina is a familiar and pleasant object for the observer. The ballerina is positioned so that one extended leg overlaps the conical fixation target. The colors of the overlapping areas are different to allow easy spacial recognition but similar enough to reduce visual clues of the actual planar movement of the ballerina during the observation of the stereo-illusion. In one embodiment the extended leg of the ballerina is black and overlaps a lilac portion of the cone and the skirt of the ballerina is lilac and overlaps the black tip of the cone.